Like all the add-ons at the Atlassian Marketplace, Email&Tasks: Jira Cloud for Gmail is set in two ways:

•  from the Atlassian Marketplace

•  from the Jira Admin page

Installation from the Atlassian Marketplace

1. Type "Email&Tasks: Jira Cloud for Gmail" in the "Search the Marketplace" field.

2. Find the Email&Tasks: Jira Cloud for Gmail add-on by SaaSJet in the search results.

3. Press on the "Try it free" or "Subscribe now" buttons.

4. Select your site on atlassian.net to install the add-on, then click "Start a free trial".

Installation from the Jira admin page

1. First, click the Apps menu and go to the Find new add-ons page.

2. Type "Email&Tasks: Jira Cloud for Gmail" by SaaSJet in the search box and then click it.

3. Click "Free trial" or "Subscribe now" to download and install the app.

4. You're all set!
   

For full use, installing the add-on connector from the Google Workspace Marketplace is also necessary. 

Also, pay attention to the Google Chrome browser extension Jira in Chrome.

You can download it from this link .

The process of setting up a browser extension >> Get started - Google Chrome Extension: Jira in Chrome